1. Field of the Invention
The invention is related to the field of nanometer-scale imprinting and, in particular, to an improved release layer for a master tool and a stamper tool used in nanometer-scale imprinting, and an improved resist material used in nanometer-scale imprinting.
2. Statement of the Problem
Magnetic disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic disk is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic disk where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Disk drive manufacturers strive to increase the recording density of drive systems. One way to increase the recording density is to pattern the surface of the magnetic disk to form discrete data tracks, referred to as discrete track recording (DTR). A magnetic disk utilizing DTR typically includes a series of concentric raised zones, which are referred to herein as pillars, providing a medium for storing data.
DTR magnetic disks are fabricated using nanoimprint lithography (NIL). Nanoimprint lithography is a high-throughput method for imprinting nanometer-scale patterns on a substrate. To imprint the nanometer-scale patterns on a substrate, a master tool is first fabricated having a desired pattern. The master tool is not typically used for imprinting an actual substrate as it can be quickly worn out when a large number of imprints are needed. The master tool is expensive and time consuming to fabricate, so the master tool is rather used to fabricate a plurality of stamper tools. The stamper tools are actually used for imprinting the substrates.
To fabricate a stamper tool, the master tool is pressed into a layer of polymer stamper resist material to imprint the inverse pattern of the master tool in the stamper resist material. Heat or ultraviolet (UV) irradiation may then be applied to the stamper resist material to harden the stamper resist material in the inverse pattern of the master tool. The master tool is then removed from the stamper resist material leaving a stamper tool having a desired pattern. The stamper tool may then be used to imprint a plurality of substrates.
To imprint a substrate, the stamper tool is pressed against a thin layer of replica resist material deposited on the substrate to imprint the inverse pattern of the stamper tool in the replica resist material. The stamper tool is then removed from the replica resist material leaving a substrate with a desired resist pattern covering the substrate. An etching process, such as Reactive Ion Etching (RIE), may then be performed to pattern the substrate according to the resist pattern. A similar process is performed to pattern many substrates using the stamper tool.
When the master tool is pressed into the layer of stamper resist material, some of the resist material may stick to the master tool. Similarly, when the stamper tool is pressed into the layer of replica resist material, some of the resist material may stick to the stamper tool. To avoid such a problem, a release layer is formed on the master tool and the stamper tool from some type of anti-adhesion material. The release layer has anti-adhesion properties (low surface energy and low friction) so that the resist material does not stick to the master tool or the stamper tool when these tools are pulled away from the resist material. One anti-adhesion material commonly used to form release layers is fluoroalkyltrichlorosilane.
One problem with the present anti-adhesion materials is that they do not effectively bond to both the master tool and the stamper tool. For example, a silane-based anti-adhesion material will effectively bond to the silanol groups on a master tool formed from Silicon (Si). However, the silane-based anti-adhesion material will not bond directly to a polymer stamper tool because the polymer material of the stamper tool does not include silanol groups as does the Si material. As a result, the release layer will not effectively adhere to the stamper tool as it does the master tool.
Another problem with present nanometer-scale processes is that the nanometer-scale patterns do not replicate with a desired consistency. For instance, assume that a hole or pillar (hole/pillar) pattern is imprinted by a stamper tool into the replica resist material on a substrate. The replica resist material is typically polymethyl methacrylate (PMMA). When the stamper tool is pulled away from the replica resist material, some of the pillars in the pattern may not be replicated at all and some of the pillars may have a height significantly shorter than desired. It is thus desirable to have substantially uniform pillar heights in a pattern in the resist material indicating that the pattern was accurately replicated.